Add GL_ANGLE_pack_reverse_row_order to command buffer

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
===================================================================
--- gpu/command_buffer/service/gles2_cmd_decoder.cc	(revision 110991)
+++ gpu/command_buffer/service/gles2_cmd_decoder.cc	(working copy)
@@ -5716,7 +5716,8 @@
     SetGLError(GL_INVALID_ENUM, "glPixelStorei: pname GL_INVALID_ENUM");
     return error::kNoError;
   }
-  if (!validators_->pixel_store_alignment.IsValid(param)) {
+  if (GL_PACK_REVERSE_ROW_ORDER_ANGLE != pname &&
+      !validators_->pixel_store_alignment.IsValid(param)) {
     SetGLError(GL_INVALID_VALUE, "glPixelSTore: param GL_INVALID_VALUE");
     return error::kNoError;
   }
@@ -5725,6 +5726,8 @@
   case GL_PACK_ALIGNMENT:
       pack_alignment_ = param;
       break;
+  case GL_PACK_REVERSE_ROW_ORDER_ANGLE:
+      break;
   case GL_UNPACK_ALIGNMENT:
       unpack_alignment_ = param;
       break;